1. Field of the Invention
This invention relates to disk head assemblies for supporting read/write heads adjacent rotating disks in disk drives and more particularly, to a base plate for attaching a load beam assembly to a head actuator arm.
2. Description of the Prior Art
Disk drives typically include a stack of spaced apart, concentric magnetic storage disks mounted on a common shaft, and an actuator arm assembly encased within a housing. The actuator arm assembly, also called a head stack assembly (HSA), comprises a plurality of arms extending into spacing between the disks. Mounted on the distal end of each arm is a resilient suspension assembly to which is attached an air bearing slider. Included in the suspension assembly is a load beam, which is mounted at one end to the actuator arm by means of a base plate, and a flexure which is attached to the other end of the load beam and pivotally supports the slider on a gimbal that keeps the slider suspended in a horizontal plane regardless of any motion of the load beam.
The load beam provides the resilient spring action that biases the slider toward the surface of a magnetic recording disk, while the flexure provides flexibility for the slider. A thin film magnetic transducer is deposited at an end of the slider to read or write on the magnetic disk.
The actuator arm and load beam elements of the head stack assembly are connected end to end by a base plate which includes a flat flange portion and a cylindrical hub portion or boss. In assembling the head stack, the hub is inserted into a load beam boss hole and the flange portion is welded to the load beam. The hub is then inserted into an actuator arm boss hole. Using a swage ball tool, pressure is applied to cause the hub to expand into the boss hole in the actuator arm, rigidly connecting the hub and attached load beam to the actuator arm boss hole. In the swaging process, a steel ball is pressed through the hub in the base plate. As the hub plastically deforms, it hardens, which is desirable for maintaining a press fit in the actuator arm boss hole.
A typical base plate is stamped in a progressive die in a sequence of forging and coining operations. The base plate is subsequently fully annealed to soften the metal which allows the material in the hub region to yield at a low stress level during a swaging operation. This permits more readily plastic deformation thus creating a greater press fit against the inner wall of the actuator arm boss hole. Since the flange as well as the hub is soft from annealing, the flange deforms easily. Deformations in the flange are transmitted to the load beam that is welded to the flange, causing undesirable fluctuations in the gram load. A prior art solution is to start with a harder base-plate material. But with a harder base-plate material, higher swaging forces are needed to cold work the hub, which in turn deforms the base plate even more severely. As the disk drive industry moves to nano and pico form factors, the effect of swaging on the load force is of even greater concern.
It is therefore an object of this invention is to provide a base plate which will yield in the hub without excessive deformation of the flange.